Mandark Astronomanov, a new student at Dexter’s school, seems to be superior to Dexter academically. Mandark forces Dexter to shut down his lab so that Mandark’s lab can gain more power. However, with the help of Dee Dee, Dexter manages to destroy Mandark’s lab.

Mandark gets inside Dexter’s computer system and creates a computer virus, so Dexter must follow him inside and kick him out from cyberspace. However, Dee Dee has other plans in mind.

Dexter creates a satellite to clean stains off of his clothes, but it goes horribly wrong when Mir space station hits the satellite that Dexter created and the satellite becomes damaged, causing the fabric beneath each stain to be eliminated as well.

Following the destruction of his lab by Dexter and Dee Dee (in the episode Dexter’s Rival), Mandark turns to magic to beat Dexter at the science fair.

After staying up late at his lab, Dexter oversleeps, waking up one minute before his school bus arrives. With no time to do his morning chores and homework, he pulls out a secret prototype device, which converts his last 30 seconds into 30 minutes.

Dexter’s newest invention looks like a hat, so Dee Dee takes it and wears it around town.

Dexter is forced to take Dee Dee to the zoo. There, she ends up trying to save an ostrich with disastrous results. Dee Dee and the ostrich switches their places.

Dexter and Dee Dee go to South America to catch the legendary chupacabra.

Rerun of the second What a Cartoon! pilot.

Monkey encounters Simion (Maurice LaMarche), an intelligent anthropomorphic chimpanzee who seeks vengeance on humans for turning him into his current state.

Dexter and Dee Dee compete against each other on a game show.

Dexter tries to move the Moon, which is blocking Saturn and its “science waves” (which is what makes it a “good day for science”).

After a crime prevention talk at school, Dee Dee, Lee Lee, and Mee Mee become crime fighters, but they unintentionally end up being neighborhood criminals.

Dexter’s father is left to watch the kids while his wife visits her sister.

After a Puppet Pals marathon, Krunk dreams the Puppet Pals are attacking puppet versions of Major Glory and Valhallen.

Dad decides to give the car a retouch, but keeps breaking things and saying he will fix it later. After having enough, he pushes the car over a cliff, and below it are other crushed cars, meaning this was not the first time.

Dee Dee’s new dance moves annoy Dexter to no end.

Created and narrated by a six-and-a-half-year-old boy named Tyler Samuel Lee, who sent a tape containing the episode’s audio to Cartoon Network,[9] the story follows Dexter and Mandark’s robot “brother” Computress teaming up to make Mandark’s head shrink.

Dexter and Dee Dee enter tryouts to become Major Glory’s sidekick. When Dee Dee wins, Dexter realizes that fancy costumes are not the only criterion to become a superhero.

Dee Dee learns a new game that can predict the future events.

When Dexter discovers that Beau, Dee Dee’s new boyfriend, has similar interests as him, Dexter tries to steal Beau’s attention from Dee Dee.

Dexter’s family must rescue him from aliens.

When Dexter learns that Dee Dee is trying to make a science project alone, he decides to help her, but she does not want his help.

When Dexter’s friends become tired of his complicated traps and cheating while playing a role-playing game, they put Dee Dee in his place. She changes the style of play, which annoys Dexter but impresses his friends.

When Dee Dee tries to cut off a piece of her hair, she accidentally cuts off one of her pigtails. Dexter gives her a potion to make her missing hair grow back. However, Dee Dee squirts too much of it in her hair, and Dexter must return Dee Dee’s hair back to normal.

Dexter finds out that all of Mandark’s plans are taken from a comic book.

Dexter becomes the stern administrator of his local library.

Dexter creates a robot to assist him, but the robot starts controlling his lab and tries to destroy Dexter.

Dexter and Dee Dee refuse to flush their dead goldfish into the toilet and are later haunted by its spirit.

Dexter and Dee Dee’s father buys a video game for them to play, but the game sucks Dexter inside when he plugs in the cartridge, and it is up to Dee Dee to bring him out.

When his mother falls ill, Dexter creates a robot to do her chores. Dee Dee gets hold of its remote control and wreaks havoc, forcing Dexter to create a second robot to counter Dee Dee’s.

Dexter and Mandark are both outperformed by a new girl at school, so they reluctantly team up to get rid of her.